I am going to take a hard line here with those being described as homeless living by the river. The term "homeless" has a meaning in society which means something different to various people. To the guys who run the Drop In Center, it means anyone without a home. To others, like me, there is a difference between a homeless person and a bum The guys living on the river sound like bums. I have little sympathy for bums. They need help, true, they don't need to be coddled like children. Worrying about hurting their feelings shouldn't be a concern when their lives are intruding on others, as is the case with living by river and dropping a load where ever you want.
I don't want a showdown. I want quiet, professional action. Ask them to leave and offer them help. Most have addiction or mental health issues. If they refuse to leave, be more forceful about asking. If they still will not go at the end of the day, move them by force. Do NOT use kid gloves, if they are not going to go willingly. Sure, it sounds brutal, but sometimes you have handle people when they are unable to handle themselves.
Some activists will howl at the moon over this. City Beat and Brian Garry likely will rumble a bit. At the end society will have a better run Tall Stacks, the bums with hopefully get the help they need. If not, they'll be crapping someplace else until they bother somebody else.